This invention relates to a gob canopy attached to the rear of a mine roof support for stabilizing and/or steering the roof support during roof-supporting operations and/or advancing movement for a longwall or shortwall mining operation.
In a longwall mining operation, a plurality of mine roof supports is arranged in a side-by-side relation and connected by double-acting piston and cylinder assemblies to a conveyor extending in front of the roof supports along the coal face being worked. The conveyor is advanced toward the receding mine face by actuating the double-acting piston and cylinder assemblies while the supports are set against the mine roof. After the conveyor is advanced, the roof supports are advanced in succession by first releasing one or more of the supports from engagement with the mine roof and then actuating the piston and cylinder assemblies to pull the mine roof support toward the conveyor. The hydraulic props of the supports are then extended until the canopy is again set against the mine roof.
Generally, a face-cutting machine travels from end-to-end along the mine face while guided and usually supported by the conveyor. The cut material is loaded on the conveyor and transported to the main entry at one end of the mine face. Two types of longwall mining operations may be carried out, namely an advancing mine face and a receding mine face. In both mining operations, the coal face extends at right angles between the entries. Coal is transferred in the main entry from a conveyor extending along the mine face to other coal-conveying equipment used to transport the coal for delivery from the mine. In these types of longwall mining operations, several roof supports with relatively long roof canopies must be advanced along the entries in conjunction with a multitude of other roof supports arranged in side-by-side relation along the path of travel by the mining machine.
The roof supports at the entries have much longer canopies to provide support for the entry roof at the side of the longwall face from a position which is generally aligned with the roof supports arranged along the mine face. T-shaped roof areas are formed by the junction of the entry roof and the roof at the longwall mine face. The entry roof is cumbersome to support because of the congestion by equipment. Also, roof supports in the entries usually have self-contained advancing mechanisms, e.g., walking beams, since there is a lack of anchors necessary for use with the same type of advancing cylinders used to move roof supports toward the mine face. The roof supports in the entries usually have canopies that extend forwardly beyond the longwall mine face into the gallery at the sides thereof. Because of the cantilevered nature of the canopy for these roof supports, the forward toe portions of the bases which rest on the floor are subjected to very high localized loading due to the force couple on the overhung or cantilevered portion of the canopy. The same type of loading also occurs with the roof supports along the mine face but smaller in magnitude. The forward toe portion of a support base is punched or sunk into the floor when the forward force couple exceeds the limit of the load-bearing capacity of the mine floor. It is disruptive and difficult to move any roof support when the toe portion is punched into the floor. Thus, even though bearing tests may be taken of a floor to determine its capacity for bearing a support, the results must show an excessively large capacity due to the greater load imposed on the floor by the forward toe portion as compared with the rear toe portion of the base of the roof support. All of the roof supports, particularly the roof supports moving along the gallery undergo lateral shifting when they are advanced, particularly when passing over an unusually rough floor area. Advancing cylinders connected to conveyor pans are used to move the roof supports along the mine face and deliver a directed pull force that frequently minimizes unwanted lateral shifting of the roof supports. Such shifting occurs to a far greater extent with supports in the gallery because the advancing mechanisms do not supply such a directed pull force.